Although there are advantages for a brushless DC motor to have larger starting torque, adjustable speed by controlling frequency, high efficiency and no pollution, etc, the power of a brushless DC motor limits its application fields directly. For a long time, a brushless DC motor whose power is under 1 KW is mainly used in the fields of model airplane, household appliances and electric bicycle. Generally, a gasoline engine or a diesel engine is used as power in the application requiring larger power. In recent years, with the rising of environmental protection consciousness to reduce the discharge of carbon dioxide and noxious gas, there is a great tendency to replace an oil-fired engine with an electric motor as power. Presently the brushless motor whose power is 3-5 Kw has appeared in the market, mainly used in the electric car with 8 seats, the golf car and the sailing yawl, etc.
At present, the large power brushless motor whose power is over 5 Kw is seldom used because of the technique of controller, battery and the radiation problem. When the power of a motor gets larger, the power which the controller is required to bear gets larger, and the power which a controller can bear depends on the power transistor. Now the problems of the power transistor and the battery of the large power motor are about to be solved, however the resulting radiating problem still hasn't been solved effectively. A large power motor can generate huge amounts of heat, and the components of the motor are easily to get burnt if the heat can't be released effectively in time.
A conventional brushless motor whose power is over 15 Kw is large-sized and heavy, and uses a liquid cooling system to solve its heat radiation problem. Its structure is complicated, that's why the application of a brushless motor whose power is over 15 Kw is rare and this kind of motor is only used in industry, while it is not applicable in the fields of manned spacecraft and skiff, etc.
Therefore, persons skilled in the art are longing for developing a brushless motor whose power is 5 Kw or over, which is suitable for manned spacecrafts and skiffs, etc.